you don't buy people. you convert people. once their converted, you can train them. you train them by buying a workshpo (sorry, had to do it), target range, or that pool thing that trains wizards. once you buy those things, you'll see flags appear on the castle towers. click on the flag to train a converted fighter to perform one of those tasks. my advice is to work first on getting all the wizards you can. after you get about 20 or so, you can start instantly converting by using the "D" spell. that will help you build your army much quicker.
oh, i forgot to tell you . . . you need to buy a temple to convert people. you can only convert one at a time when you bring them into your castle. you cannot pick up the big guys. you can, however, convert them instantly with a spell when you get enough wizards.
i currently have over 7 million points and nearly 2 million spendable points after each stage w/o actually participating. yeah, i'm cool.
man, i need help.